Lecture 13 3/27/25 Flashcards
What are the characteristics of feline hyperthyroidism?
-most common feline endocrine disorder
-commonly seen in GP
What are the characteristics of feline hyperthyroidism pathophysiology?
-thyroid adenomatous hyperplasia
-foci and nodules of hyperplastic tissue
-multiple, bilateral, benign masses are most common
-occasionally ectopic
-malignant carcinoma is rare
What are the suspected roles of genetics in feline hyperthyroidism risk?
-decreased risk seen in siamese and himalayan cats
-increased risk seen in non-purebred cats
-decreases in G inhibitory proteins lead to increased stimulation of growth
What are the suspected environmental risk factors for feline hyperthyroidism?
-canned food with pop top lids
-iodine
-BPA and phthalates
-flame retardant PBDEs
-other goitrogens
What is the signalment for feline hyperthyroidism?
-middle to older age cats; typically > 10 yrs
-any breed
-any gender
What are the most common clinical signs of feline hyperthyroidism?
-weight loss (most common)
-vomiting
-PU/PD
-hyperactivity/restlessness
-diarrhea
What are other potential clinical signs of feline hyperthyroidism?
-anorexia
-lethargy
-tremors/weakness
-dyspnea/panting
-heat and stress intolerance
-thyroid storm
What is thyroid storm?
rare, life-threatening secondary rapid T4 increase
Why is it important to palpate the entire cervical region in cats with suspected hyperthyroidism?
many cats with have palpable thyroid nodules
What are other findings on physical exam besides a palpable nodule in cats with hyperthyroidism?
-cachexia/thin body condition
-tachycardia
-systolic murmur
-arrhythmia
-effusion
-edema
-fundic abnormalities
-abnormal blood pressure
Which cardiac diseases can be seen with hyperthyroidism?
-reversible hypertrophy secondary to hyperthyroidism
-concurrent primary hypertrophic cardiomyopathy
What should be included in the diagnostic workup of a suspected hyperthyroid cat?
-CBC/chem/UA
-thyroid hormone screening
-BP measurement
-thoracic rads
-ECG
-echo
-possibly additional imaging
-evaluation of other conditions
What are the findings on chem in hyperthyroid cats?
-elevated hepatic enzymes, esp. ALT
-reversible, mild to moderate enzyme elevations
-stress hyperglycemia
-possible azotemia
-possible hyperphosphatemia
What are the findings on UA in hyperthyroid cats?
-decreased USG
-possible/asymptomatic UTI secondary to decreased hsot defenses
What are the characteristics of hyperthyroidism and the kidneys?
-older cats often have decreased kidney function or CKD
-hyperthyroid state increases renal blood flow and enhances GFR
-renal failure can be masked by the hyperthyroid state
How does survival rate differ between cats with concurrent hyperthyroidism and kidney disease vs cats with just hyperthyroidism?
cats with both conditions do not live as long
Which diagnostics are done to assess the cardiovascular system in hyperthyroid patients?
-radiographs
-ECG and/or echo
-BP measurements
What findings can be seen on thoracic rads in hyperthyroidism patients?
-more prominent cardiac silhouette
-heart failure
-lung nodules
How is feline hyperthyroidism diagnosed?
single elevated serum TT4 is diagnostic
What are the limitations of TT4 measurement?
-daily and hourly fluctuations
-can be normal in early or mild hyperthyroidism cases
-can be depressed by non-thyroidal illness
How should increased fT4 be interpreted, based on TT4 measurement?
-low to low-normal TT4 with increased fT4: non-thyroidal illness
-high-normal to high TT4 with increased fT4: hyperthyroidism
What are the characteristics of the T3 suppression test?
-administer T3 and measure T3 and T4 (and possibly TSH)
-normal cats should have low TSH and T4 due to negative feedback
-hyperthyroid cats will have minimal decreases in T4
What are the characteristics of TSH measurement?
-feline TSH can be measured with canine kits
-not routinely done
-often reserved for challenging cases
What are the characteristics of thyroid scintigraphy?
-radioactive marker identifies functional thyroid tissue
-confirms diagnosis of hyperthyroidism
-can detect unilateral vs bilateral, benign vs malignant, ectopic, and metastatic dz
-used prior to radioiodine treatment to plan dosing
What are the reversible treatment options for hyperthyroidism?
-anti-thyroid medications
-dietary management
What are the definitive treatment options for hyperthyroidism?
-radioiodine
-surgery
-ablative injections
What are the uses of reversible hyperthyroidism treatments?
-short term therapy as a trial period or prior to definitive treatment
-long term therapy if well tolerated
What are the characteristics of dietary hyperthyroidism control?
-cats must only eat iodine-restricted food
-typically see T4 decreases within 2 to 6 months
-may not fully cure clinical signs/effects
What are the characteristics of methimazole?
-inhibits thyroid hormone synthesis
-can be given orally or transdermally
-can use dose escalation to monitor for decompensations in renal function
What are the adverse side effects of methimazole?
-hematologic abnormalities
-GI upset
-facila/neck excoriations
-hepatotoxicity
-weakness or myasthenia gravis
What should be monitored in patients on methimazole?
-CBC
-T4
-liver enzymes
-renal function
What is the renal function assessment for hyperthyroid cats on methimazole?
-if T4 normalizes and kidneys remain normal, treatment can be continued OR definitive treatment can be done
-if T4 normalizes but kidneys worsen or cat worsens clinically, methimazole should be reduced and cat rechecked
-if T4 is still high and kidneys remain normal, methimazole should be increased and cat rechecked
What is the goal of definitive hyperthyroidism treatment?
remove or destroy all hyperfunctioning tissue permanently
What are the characteristics of radioiodine?
-radioactive iodine concentrates in hyperplastic thyroid tissue regardless of location within body
-normal thyroid tissue is “spared” due to atrophy
-fixed/calculated dose is administered
-single SQ dose
-initially expensive
What are the considerations with radioiodine?
-limited to licensed vets and facilities
-should discontinue reversible treatments for two weeks prior to administration
-strict isolation period required for 1 to 3 weeks
-most respond well to one treatment; repeat treatment may be needed
What are the advantages of surgical thyroidectomy?
-relatively short procedure
-effective for localized tissue
-rapid return to euthyroid state
-no special licensing or isolation requirements
What are the disadvantages of surgical thyroidectomy?
-anesthetic and surgical risks
-complications including hypoparathyroidism, hypothyroidism, and laryngeal paralysis
-higher recurrence rate than radioiodine
-initially expensive
What are the characteristics of percutaneous injections?
-can be done with ethanol or heat methods
-better for unilateral dz
-require anesthesia
-ultrasound guided with specialized personnel
-can lead to laryngeal nerve paralysis, voice changes, and tissue damage
What are the characteristics of azotemia?
-can develop within 6 months of hyperthyroidism treatment
-related to hypothyroidism and decreased GFR
-want to evaluate TT4 and TSH alongside kidney eval.
What are the characteristics of hypertension?
-25% of normotensive cats prior to hyperthyroidism tx will develop hypertension
-want to evaluate BP in all cats at the start of treatment and then every 3 to 6 months
-best to use doppler
What are the characteristics of canine hyperthyroidism?
-often secondary to thyroid neoplasia
-can occur with excess thyroid hormone in diet
-typically see malignant thyroid carcinomas
-diagnosis via thoracic rads, scintigraphy, and histopath.
-treated with surgical excision
